1. Technical Field
The present invention relates to a common mode filter.
2. Description of the Related Art
Recently, electronic devices such as a cellular phone, a home appliance, a personal computer (PC), a personal digital assistant (PDA), a liquid crystal display (LCD), and the like, have been gradually digitalized and a speed of the electronic devices has gradually increased. Since these electronic devices are sensitive to stimulus from the outside, in the case in which small abnormal voltage and high frequency noise introduced into the electronic devices from the outside into an internal circuit, a circuit may be damaged or a signal may be distorted.
An example of a cause of the above-mentioned abnormal voltage and noise includes lightning, electrostatic discharge charged in a human body, switching voltage generated in the circuit, power noise included in power supply voltage, an unnecessary electromagnetic signal, electromagnetic noise, or the like. As a unit for preventing the above-mentioned abnormal voltage and high frequency noise from being introduced into the circuit, a common mode filter has been used.
A general structure of a common mode filter according to the related art will be described with reference to Patent Document 1. The common mode filter according to the related art has a structure in which a pair of conductor coils magnetically coupled to each other is formed on a magnetic substrate and is enclosed by an insulating resin. That is, the common mode filter has a structure in which the magnetic substrate and an insulating layer are stacked in view of an appearance.
However, in the general common mode filter according to the related art as disclosed in Patent Document 1, since a primary coil and a secondary coil are formed on different layers, there is a limitation in slimming the common mode filter.
In addition, since one ends of the primary and secondary coils are positioned at the center of a winding region, a lead wire should be provided on a separate layer in order to connect one ends of the first and secondary coils to external electrodes. Therefore, it is difficult to slim the common mode filter, and parasitic capacitance is generated between the lead wire and the coils to deteriorate performance of the common mode filter.